Dominant role of OH− and Ti3+ defects on the electronic structure of TiO2 thin films for water splitting

Abstract

Anatase/rutile constituting TiO₂ thin films were prepared by sputter deposition, and the influence of the post-annealing step with a narrow window at 200 °C revealed a gaining factor of 5 in H₂ production. An in-depth analysis of the photocatalytic performance revealed the dominant role of intermediate states rather than the heterocrystalline nature and the mesoscale structure. Structural, chemical and optical investigations based on scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible spectroscopy and photoluminescence supported by ab initio calculation correlated the H₂ production with the dual presence of OH⁻ and Ti³⁺ defects in the form of titanium interstitial atoms. In addition, steady-state photoluminescence measurements determined the chemically active role of ethanol, commonly used as a hole scavenger, in inducing deep hole traps upon dissociation on the surface. These results give new directions for the design of TiO₂ based photocatalytic systems for light-driven H₂ production through water splitting, guided by a detailed description of defects present on the electronic structure and their chemical identification.